There are digital copiers that append attribute information for every pixel of image data and execute image processing in accordance with this attribute information. For example, a text/image flag and chromatic color/achromatic color flag are appended as attribute information to a copy image that has been read in by a scanner or the like. Alternatively, a mode is switched between a photographic paper mode or a non-photographic paper mode on a per-page basis in accordance with the operating mode of read-in processing and is appended as an attribute. Further, a text/image flag, chromatic color/achromatic color flag and vector flag, etc., are appended as attribute information to PDL data that is input from a computer, by way of example.
In image processing, an improvement in image quality is achieved by changing over the processing method of the image processing based upon such attribute information. For example, color printing and monochrome printing are switched between in accordance with the chromatic color/achromatic color attribute, which is one item of attribute information, and halftone processing is switched between the error diffusion method and screen method based upon the text/image flag [see Japanese Patent Application Laid-Open No. 09-282471 (Patent Reference 1)].
A digital copier has an N-in-1 copying function for reducing the size of an image read in by a scanner, fitting a plurality of images on a single page and printing out the images on a single page. (If paper of large size is used, this function can be implemented without reducing image size. In this specification, however, the function will be referred to as “N-in-1 copying” for the sake of convenience). In a case where the N-in-1 copying function is used, a problem which arises is that the appropriate processing cannot be applied for each and every image read in. For example, consider the execution of processing for an automatic color/monochrome decision (a function for determining whether a color image to be copied contains a color component other than black, and appending an achromatic color attribute if it is determined that the image does not contain a component other than black) or for automatic under-color removal (a function for removing the under-color of a document) when a copy is to be made. If image processing such as the automatic color/monochrome decision or automatic under-color removal is executed after a plurality of images are read in and the images combined as images formed on a single sheet of paper, the automatic color/monochrome decision or automatic under-color removal will be executed per page on which the plurality of read images have been made to fit. Since there is the possibility that there will be a disparity in whether an image is monochrome or color or in the under-color for every page of the document that has been read in, it is also possible that an image of a quality different from that which would be obtained when a single image alone is laid out on a single page will be printed. For example, if a monochrome image and a color image are laid out on one page, the image decided as that of the overall page is the color image and the portion that is the original monochrome image is processed as process black combined with a color component, as a result of which the image may be made gray in color. Further, if an image that has been printed on white paper and an image that has been printed on colored paper are scanned and laid out on one page, the image portion that was printed on the colored paper will still contain the under-color component.